1. Field of the Invention
The invention relates generally to seismic exploration. More particularly, the invention relates to a method for deployment of a seismic recorder array with removable data recorders and acquisition of marine seismic data.
2. Description of the Related Art
Marine seismic exploration utilizes acoustic energy source generators for transmitting acoustic energy (also referred to as seismic energy) through subsurface geologic formations. The acoustic energy is transmitted along shot lines in the desired survey region. The transmitted acoustic energy propagates downwardly through the subsurface as acoustic waves (also referred to as seismic waves or signals). The transmitted acoustic waves are reflected by the subsurface formations and boundaries. The reflected acoustic waves propagate upwardly and are detected with hydrophones or geophones. Data from adjacent shot lines are processed to construct an image of the subsurface geologic formations.
In marine seismic exploration, a marine vessel is used to deploy seismic data recorders to the seafloor. In one existing method, a marine vessel tows one or more seismic streamer cables along a selected survey line. Each streamer contains multiple hydrophones which receive the reflected seismic waves. The hydrophones are wired together in receiver groups spaced along the streamer. In another existing method, interconnected seismic data recorders are placed directly on the seafloor. The seismic data recorders are interconnected by reinforced cables that provide power and transmit data from the seismic data recorders to a remote storage device. Because this system relies on cables for power and data transmission, any damage to the cables or connectors prevents the recording of data and contributes significant downtime and increased survey cost while the system is retrieved, repaired and redeployed. Also, the data and power cables add significant weight to the system which, combined with the reliability concerns, effectively prevents such systems from being deployed in deep water.
U.S. Pat. No. 6,024,344 to Buckley et al. discloses a system wherein autonomous nodal recorders are attached to a main cable by individual tethers. The tethers can wrap around and get tangled in the main cable during deployment and potentially compromise data quality. Also, because the seismic recorders attach to the main cable only at a single point, the recorders will land on the ocean bottom at a completely random orientation relative to the other recorders and the survey geometry in general.